3,584 research outputs found
"Cold Melting" of Invar Alloys
An anomalously strong volume magnetostriction in Invars may lead to a
situation when at low temperatures the dislocation free energy becomes negative
and a multiple generation of dislocations becomes possible. This generation
induces a first order phase transition from the FCC crystalline to an amorphous
state, and may be called "cold melting". The possibility of the cold melting in
Invars is connected with the fact that the exchange energy contribution into
the dislocation self energy in Invars is strongly enhanced, as compared to
conventional ferromagnetics, due to anomalously strong volume magnetostriction.
The possible candidate, where this effect can be observed, is a FePt disordered
Invar alloy in which the volume magnetostriction is especially large
Phase transitions in spin-orbital coupled model for pyroxene titanium oxides
We study the competing phases and the phase transition phenomena in an
effective spin-orbital coupled model derived for pyroxene titanium oxides
ATiSi2O6 (A=Na, Li). Using the mean-field-type analysis and the numerical
quantum transfer matrix method, we show that the model exhibits two different
ordered states, the spin-dimer and orbital-ferro state and the spin-ferro and
orbital-antiferro state. The transition between two phases is driven by the
relative strength of the Hund's-rule coupling to the onsite Coulomb repulsion
and/or by the external magnetic field. The ground-state phase diagram is
determined. There is a keen competition between orbital and spin degrees of
freedom in the multicritical regime, which causes large fluctuations and
significantly affects finite-temperature properties in the paramagnetic phase.Comment: 4 pages, 6 figures, proceedings submitted to SPQS200
Inhomogeneous Condensates in Planar QED
We study the formation of vacuum condensates in dimensional QED in the
presence of inhomogeneous background magnetic fields. For a large class of
magnetic fields, the condensate is shown to be proportional to the
inhomogeneous magnetic field, in the large flux limit. This may be viewed as a
{\it local} form of the {\it integrated} degeneracy-flux relation of Aharonov
and Casher.Comment: 13 pp, LaTeX, no figures; to appear in Phys. Rev.
Symmetry of Traveling Wave Solutions to the Allen-Cahn Equation in \Er^2
In this paper, we prove even symmetry of monotone traveling wave solutions to
the balanced Allen-Cahn equation in the entire plane. Related results for the
unbalanced Allen-Cahn equation are also discussed
Law Behind Second Law of Thermodynamics --Unification with Cosmology--
In an abstract setting of a general classical mechanical system as a model
for the universe we set up a general formalism for a law behind the second law
of thermodynamics, i.e. really for "initial conditions". We propose a
unification with the other laws by requiring similar symmetry and locality
properties.Comment: 17 page
Orbital and spin interplay in spin-gap formation in pyroxene titanium oxides ATiSi2O6 (A=Na, Li)
Interplay between orbital and spin degrees of freedom is theoretically
studied for the phase transition to the spin-singlet state with lattice
dimerization in pyroxene titanium oxides ATiSi2O6 (A=Na, Li). For the quasi
one-dimensional spin-1/2 systems, we derive an effective spin-orbital-lattice
coupled model in the strong correlation limit with explicitly taking account of
the t_2g orbital degeneracy, and investigate the model by numerical simulation
as well as the mean-field analysis. We find a nontrivial feedback effect
between orbital and spin degrees of freedom; as temperature decreases,
development of antiferromagnetic spin correlations changes the sign of orbital
correlations from antiferro to ferro type, and finally the ferro-type orbital
correlations induce the dimerization and the spin-singlet formation. As a
result of this interplay, the system undergoes a finite-temperature transition
to the spin-dimer and orbital-ferro ordered phase concomitant with the
Jahn-Teller lattice distortion. The numerical results for the magnetic
susceptibility show a deviation from the Curie-Weiss behavior, and well
reproduce the experimental data. The results reveal that the Jahn-Teller energy
scale is considerably small and the orbital and spin exchange interactions play
a decisive role in the pyroxene titanium oxides.Comment: 13 pages, 9 figures; final version. Text, Fig.1, and references are
revised. To appear in Phys. Rev.
Initiation of skin basement membrane formation at the epidermo-dermal interface involves assembly of laminins through binding to cell membrane receptors
To study the mechanism of basement membrane formation, we determined by immunochemistry temporal and spatial expression of laminin-5 (Ln-5), laminin-1 (Ln-1) and their integrin receptors during early skin morphogenesis. A 3-dimensional skin culture was used that allows the study of the sequential molecular events of basement membrane formation at the epidermodermal interface. During early anchorage of keratinocytes to the extracellular matrix there is expression of Ln-5, BP-230 antigen and α3, β1 integrin subunits. During epidermal stratification and prior to the formation of the lamina densa there is assembly of Ln-5, Ln-1, collagen IV and nidogen accompanied by keratinocyte basal clustering of α2, α3, α6, β1, and β4 integrin subunits. The assembly pattern of Ln-1 and Ln-5 can be disturbed with functional antibodies against the β1 (AIIB2) and α6 (GoH3) integrin subunits. Ln-1 assembly can also be disturbed with antibodies against its E8 domain and by competitive inhibition with a synthetic peptide (AG-73) derived from its G-4 domain. Quantitative RT-PCR showed that the dermis contributes about 80% of the laminin γ1 chain mRNA while 20% is produced by the epidermis which emphasizes its dual tissue origin and the major contribution of the mesenchyma in laminin production. The laminin γ2 chain mRNA, present in Ln-5, was mostly of epidermal origin. This study presents evidence that during the initiation of basement membrane formation, laminins bind to keratinocyte plasma membrane receptors and thus may serve as nucleation sites for further polymerization of these compounds by a self-assembly process.</p
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